This invention relates to an optical printer suitable for use for, for example, a color video printer or the like, and more particularly to an optical printer wherein a plurality of filters are selectively alternated or changed with each other with respect to a common write source as desired.
One of optical printers which have been conventionally proposed is disclosed in Japanese Patent Application No. 276234/1991 by the assignee, which is constructed in such a manner as shown in FIG. 10. More particularly, the optical printer proposed includes a fluorescent luminous tube 100 acting as a write head. The fluorescent luminous tube 100 includes an envelope 103 constructed of a light-permeable substrate 101 and a casing 102 of a box-like shape scaledly joined to the substrate 101 and is evacuated to a high vacuum.
The substrate 101 is formed on an inner surface thereof with luminous sections each including an anode conductor and a phosphor layer deposited on the anode conductor. The phosphor layer is formed of a ZnO:Zn phosphor material. The luminous sections each are constituted by a plurality of luminous dots arranged at predetermined pitches in a main scanning direction. Three such luminous sections 200(R), 200(G) and 200(B) (200 (R, G, B)) are arranged in a sub-scanning direction.
The envelope 103 is provided therein with a Plurality of second control electrodes 104 so as to be positioned below the luminous sections 200 (R, G, B) and in a manner to be allotted to every luminous dot. The fluorescent luminous tube 100 also includes a common first control electrode 105 arranged below the second control electrodes 104 and formed in an electrically integral manner. Further, the fluorescent luminous tube 100 includes filamentary cathodes 106 arranged below the first control electrode 105 so as to extend in the main scanning direction for each of the luminous sections 200 (R, G, B).
The substrate 101 is provided on an outer surface thereof with a red filter r, a green filter g and a blue filter b in a manner to face the luminous sections R, G and B, resulting in three primary luminous colors of red, green and blue being taken out of the phosphor layers of the luminous sections. A luminous spectrum of the ZnO:Zn phosphor corresponds to a green color having not only a peak wavelength of 505 nm but a wide wavelength range between about 430 nm and 640 nm, so that use of the red, green and blue filters r, g and b permits the three primary luminous colors of red, green and blue to be taken out of the single phosphor.
The conventional optical printer also includes three lens systems 107 arranged adjacent to the filters r, g and b of the fluorescent luminous tube 100, respectively. Thus, light emitted from each of the luminous dots of the luminous sections 200 (R, G, B) is guided through each of the red, green and blue filters r, g and b to each of the lens systems 107, to thereby be focused at a predetermined position on a film 108 which is a written medium.
The print head thus including the fluorescent luminous tube 100 and lens systems 107 may be moved in the sub-scanning direction by means of a drive mechanism (not shown).
Driving of the optical printer thus constructed is carried out by scanning the luminous dots of the luminous sections 200 (R, G, B) of the fluorescent luminous tube 100 in order and applying a positive print signal to the second control electrodes 104 corresponding to the luminous sections in synchronism with the scanning. The first control electrode has a positive voltage constantly applied thereto to accelerate electrons emitted from the filamentary cathodes 106, thereby preventing any display defect due to application of a negative voltage to the second control electrodes 104 in correspondence to a non-luminous section.
The print head is moved in the sub-scanning direction indicated by an arrow in FIG. 10 in conformity with driving of the fluorescent luminous tube 100 for luminescence, to thereby focus light of each of the luminous colors at the same position on the film 108, resulting in a color image desired being formed on the film 108.
In the conventional optical printer described above which is so constructed that the filters r, g and b are securely provided on the luminous sections 200 (R, G, B) arranged in three lines to obtain light of each of the three primary colors, arrangement of the luminous sections in proximity to each other causes light emitted from each of the luminous sections to enter the filter of the luminous sections adjacent thereto, leading to color mixing. Thus, the conventional optical printer requires to increase intervals between the luminous sections to a degree sufficient to prevent the color mixing, resulting in failing in down-sizing thereof. Also, such an increase in interval between the luminous sections fails to permit light emitted from the three-line luminous sections to be satisfactorily formed into an image by means of only one optical system, so that it is required to separately arrange the optical system for every line. This renders down-sizing of the optical printer further difficult and causes an increase in manufacturing cost.